1. Field of the Invention
This invention relates generally to devices which grip tubular members, such as drill pipe, and, more particularly, to devices which hold one segment of pipe immobile while another segment of pipe is connected or disconnected.
2. Prior Art
Pipe tongs are employed in the oil and gas industry to grip and rotate drill pipe. Some operate manually, while others are power assisted. It is necessary to grip drill pipe with extremely high compressive forces while applying a high degree of torque in order to break apart or tighten threaded pipe connections. In order to develop these forces, power tongs have been designed for gripping and rotating pipe. Back-up power tongs have been designed to hold one joint or segment of pipe while power tongs grip and rotate the adjacent joint of pipe. As can be seen, the gripping force of the back-up power tongs must be at least equal to that of the associated power tongs. Examples of power tongs and back-up tongs may be seen in the following U.S. Patents:
U.S. Pat. No. 4,290,304 PA0 U.S. Pat. No. 4,404,876 PA0 U.S. Pat. No. 4,082,017 PA0 U.S. Pat. No. 4,084,453 PA0 U.S. Pat. No. 4,089,240 PA0 U.S. Pat. No. 3,023,651
While back-up power tongs must develop a significant gripping force, rotary action is not required. The combination rotary/gripping action of power tongs has historically been produced by a cam assembly. Prior art back-up power tongs have also employed cam action to grip and hold pipe. As can be seen by referring to U.S. Pat. No. 4,290,304, cam action has also been employed to impart gripping forces in back-up power tongs. The assemblies comprising prior art back-up power tongs have heretofore been complicated and required a conversion of rotative forces to compressive forces, resulting in heavy, inefficient and expensive devices.
As can be seen in the above listed patents, the actual contact with the pipe is accomplished through the use of die inserts which are pressed into some type of jaw member. When the power tongs are in operation the die inserts are urged against the drill pipe and torque is applied. Examples of various configurations of die inserts may be found in FIG. 4 of U.S. Pat. No. 4,404,876 (see reference numerals 144,148 and 149), FIG. 5 of U.S. Pat. No. 4,082,017 (see reference numeral 34), and in FIGS. 4 and 5 of U.S. Pat. No. 4,290,304 (see reference numeral 92). As can be seen, the die inserts are relatively narrow in comparison to the jaw members to which they are attached, as well as to the total area of pipe covered by the jaw members. The die inserts are most commonly held in place through a dovetail key arrangement. Those die insert configurations illustrated above are virtually a standard in the industry.
Problems have developed with the above mentioned jaw/die configurations. The small wearing surfaces of prior art dies result in tremendous pressures (per unit of area) being applied to the drill pipe. These pressures result in deformation of the pipe, which in turn results in down time and pipe replacement costs. This is especially true in deep water drilling operations where lightweight pipe must be utilized. Also, as torque is applied, the dovetail keyway of prior art dies will wear due to the small surface area which must bear the torque, necessitating expensive replacement of the entire jaw/die assembly. Because of the small wearing surface of the dies, they are also prone to quickly wear out. The above problems were necessitated by the belief that the die size must remain small in comparison to the jaw member in order to provide the necessary bulk to resist the amount of torque which is applied to the pipe.